Is there a way to adjust vimdiff's line position for a change?

Question

I have fixed some indentation issues in my project and I'm looking at the vimdiff output for the before and after. I notice that vimdiff seems to be very confused as to what the actual changes are, rendering a pretty much useless output in this case:

For example, it seems to think that the very first line is a newly added line:

<div class="text-xs-center p-4">

In reality, all that has changed is the indentation. Vimdiff is not recognizing the changes properly.

In another, similar file, the diff works much better:

I think the difference is that in the second file I did not remove the first line break.

Is there a way to manually fix this sort of thing, so that the diff shows properly? I don't want to change either file, the changes are correct. But I'd like to tell vimdiff that it's comparing the wrong lines to one another.

Is this possible?

Answer 1

The underlying diff tool compares individual lines, regardless of whether "only" indentation changed, or something more fundamental. As in your first case, there's one extra unindented line, so diff recognizes that as unchanged, and this messes up the entire diff.

If you want to ensure that only indentation got changed, you can ignore whitespace changes via

:set diffopt+=iwhite

Then, the diff should show no changes at all (or, in your first example, only the added line 5).

Maybe there are also other diff utilities that more intelligently handle these cases. If you find such tool, you can configure Vim to use it via 'diffexpr'.